Production of dienes, resin-forming aromatic hydrocarbons and nonresin-forming aromatic hydrocarbons



N. K. CHANEY ET AL 2,423,375v

July. 1, 1-947.

PRODUCTION OF DIENES, RESIN-FORMING AROMATIC HYDROCARBONS AND NONRESIN-FORMING AROMATIC HYDROCARBONS Filed Dec. 29, 1942 2 Sheets-Sheet 1 y 1947- N. K. CHANEY ET AL 2, 23,375 PRODUCTION OF DIENES, RESIN-FORMING AROMATIC HYDROCARBONS AND NQNRESIN-FORMINCT AROMATIC HYDROCARBONS Filed Dec. 29, 1942 2 Sheets-Sheet 2 Patented July 1, 1947 PRODUCTION OF DIENES, RESIN-FORMING AROMATIC HYDROCARBONS AND NON- lggiIgI-FORMING AROMATIC HYDROCAR- Newcomb K. Chaney, Moylan, Pa., and Edwin L. Hall, Manchester, N. 11., assignors to The tion of Pennsylvania Application December 29, 1942, Serial No. 470,462

United Gas Improvement Company, a corpora- This invention pertains generally to the production of valuable hydrocarbons from petroleum oil by pyrolysis and pertains particularly to the production, in the manufacture of dienes, of rel- 4 Claims. (Cl. 260-666) In both instances, the desideratum is to conduct the decomposition of the petroleum oil so as to avoid the production of large quantitie of resin-forming hydrocarbons.

In the case of combustible gas for distribution,

atively' large quantities of resin-forming and 5 non-resin-forming aromatic hydrocarbons, and the presence of relatively large quantities of particularly benzene, toluene, xylene, and styrene resin-forming hydrocarbons is highly undesirable of improved quality. since these hydrocarbons have a propensity to Among the-aromatic resin-forming hydrocarform resins throughout the gas distribution sysbons produced are compounds such as styrene, l0 tem and are responsible for the stoppage of gas methyl styrene, indenes, and material boiling beappliance valve orifices, causing the extinction of tween 210 C. and 450 C., and among the nonburners such as pilot burners and the malfuncresin-forming aromatic hydrocarbons produced tioning of'automatic appl n are compounds such as benzene, toluene, xylenes, Likewise in the case of motor fuels, the presnaphthalene, andalkyl naphthalenes such as ence of resin-forming hydrocarbons is highly unmethyl naphthalene, anthracene, etc. desirable because of their interference with the Examples of dienes produced are butadiene, proper operation of internal combustion engines. cyclopentadiene, dicyclopentadiene, isoprene and This invention as distinguished from the piperylene. processes of the prior art is directed to the pro- The invention also involves the production of duction, in the manufacture of dienes from cerother non-aromatic hydrocarbons such as isotain petroleum oils, of a relatively larger total butylene, as well as other aromatic hydrocarbons quantity of non-resin-forming aromatic hydroboiling above 200 C. at atmospheric pressure and carbons, and resin-forming aromatic hydrocarcontained in the dead oil and heavy tars. bons of improved quality.

The outstanding importance of the invention More particularly stated the invention comat the present time lies in its production (1) of prises (1) the selection of a petroleum oil capable both butadiene and styrene which are components on controlled pyrolysis, preferably in the presence of synthetic rubber; (2) of nitration grade of certain added aromatic hydrocarbon material t luene; (3) of improved qu l y ne; and to be hereinafter'defined, of producing in addi- (4) of various other resin-forming and non-resin tion to high yields of dienes, such as butadiene, forming materials of strategic importance. relatively large yields of aromatic hydrocarbons Normally in the manufacture of oil gas, pecomprising alkylated and/or alkenated aromatic troleum oil is pyrolytioally decomposed a i hydrocarbons and including relatively large yields temperatures and frequently under conditions of of styrene, methyl styrene, indene and aromatic reduced partial pressures resulting from the resin formers boiling above 210 C., as well as presence of large volumes of other gases such toluene, xylene and aromatic solvent oils boilas steam or water gas, the latter being a mixing above 210 C., of improved quality; and (2) ture of carbon monoxide and hydrogen. The the pyrolysis preferably in the presence of said products range all the way from hydrogen and added aromatic hydrocarbon material, of said normally gaseou hydrocarbons which are conselected oil or a desired cut or cuts therefrom densible with difiiculty to materials of extremely under controlled conditions to be set forth herelow vapor pressure, such as the less volatile coninafter. stituents of tar, for example, pitch. A com Said certain added aromatic hydrocarbon masiderable quantity of carbon may also be proterial comprises one or more of benzene, and duced. lower alkylated benzenes such as toluene, the

These prior art processes are conducted with xylenes, ethyl benzene, isopropyl benzene, etc. either of two urposes in mind, namely, (1) the Preferably any alkyl group contains less than production of large volumes of combustible gas four carbon atoms, and more preferably less than to be distributed as citygas, or (2) the productwo carbon atoms such as is the case with toluene tion of motor fuel. and the y Of these materials benzene, toluene and the xylenes are preferred, with benzene itself, or a mixture predominantly benzene still more preferred.

It is found that the quantitative production of the individual above-mentioned alkylated and/or alkenated aromatic hydrocarbons including aromatic resin-forming hydrocarbons varies widely with the use of different petroleum oils, and that certain physical and chemical characteristics of a petroleum oil, or combinations of these characteristics, may be employed as indices to measure the ability of said petroleum oil to quantitatively produce these compounds under carefully controlled conditions of pyrolysis.

For example when a petroleum oil is selected which may be classed as predominately naphthenic as determined by any one or more of a number of chosen methods of classification to be hereinafter more particularly set forth, for instance, by the method of classification described in Bureau of Mines Bulletin #291, dated September 1928, as modified by Bureau of Mines Report of Investigations 3279, these desired compounds may be produced in considerably reater quantity than when an oil which may be classed as predominantly parafllnic or intermediate is employed. Reference is here made to our copending application Serial Number 372,074, filed December 28, 1940, which has matured into Patent 2,383,772, granted August 28, 1945, and in which a method for pyrolyzing naphthenic petroleum oil is described and claimed.

This invention is directed to the pyrolysis of predominantly paraffinic or intermediate oils under conditions such that results approaching those attained with a predominantly naphthenic oil may be secured, together with the production of substantially higher relative yields of dienes. This is accomplished by causing said pyrolysis of said parafiinic and/or intermediate oils to take place under controlled conditions preferably in the presence of said certain added aromatic hydrocarbon material.

An added advantage of the invention is that it makes available on a practicable scale for the purposes intended, oils which are classed as predominantly parafiinic or intermediate in character, since such oils may be pyrolyzed in accordance with this invention with the production of relatively larger quantities of alkylated and/or alkenated aromatic hydrocarbons of improved quality with the very substantial reduction or complete elimination of the extremely distressing tar emulsion difficulties normally attendant upon condensation in the presence of steam of the products of the pyrolysis of such oils in an intermediate cracking range, that is, between that normally employed for the production of combustible gas and that normally employed for the production of motor fuel.

In carrying out the invention the selected oil is pyrolytically decomposed preferably in the presence of said added aromatic hydrocarbon "material in vapor phase and in an atmosphere diluted preferably with a radially condensible gas (in addition to gases produced from said added aromatic hydrocarbon material), such as steam, which together with any of said added aromatic hydrocarbon material employed is preferably present in sufficient quantity to materially reduce the partial pressures of the oil vapors.

Examples of suitable ratios of readily condensible diluent are 1 part of steam to 1 part of oil by weight; 1 part of steam to 2 parts of oil by weight and 1 part of steam to 3 parts of oil by weight; although lower ratios may be employed.

Preferably however the volumetric vapor phase dilution is at least equivalent to that produced by the pyrolysis of 2 parts of oil in the presence of 1 part of steam by weight.

Higher ratios than those given may also be employed. Higher steam ratios tend to increase the yield of dienes, whereas lower steam ratios while not favoring as high a yield of dienes, do not interfere with high yields of certain other valuable products. I

The use of water gas in large quantities as a diluent is preferably avoided among other reasons, because of its relatively high concentration of hydrogen. Thus, we prefer to restrict the presence of any blue water gas to below 35 cubic feet per gallon of oil pyrolyzed and more preferably to below 25 cubic feet per gallon of oil pyrolyzed, said cubic feet being taken as if measured at a pressure of 760 mm. Hg and a temperature of 60 F.

Generally speaking, the preferred operating conditions are of a cyclic character such as is characterized by the conventional cyclic gas making processes.

Also the process is preferably conducted with total pressures at atmospheric or near atmospheric pressure, although other pressures may be employed.

Additionally the environment of the oil pyrolysis is arranged so as to provide for relatively homogeneous cracking. Homogeneous cracking is defined herein to embrace conditions such, for instance, as concentration of oil vapors, space velocity, turbulence, surface-volume relationships of the interior of the cracking vessel or vessels and character of heated surfaces which are such that in any given plane normal to the flow of materials, the materials throughout the plane have previously had substantially the same opportunity to be heated and to undergo the alternate decompositions and syntheses which comprise cracking and which progress toward products of greater thermal stability under the enviromnent obtaining.

Other conditions being fixed, variation of any one of the following factors in the direction cited is considered to tend toward less homogeneity in the cracking operation; (1) decreased surface/volume ratio of the cracking vessels beyond the vaporizing zone; (2) reduced atomization of the oil; (3) increased impingement of oil on highly heated surfaces prior to vaporization; (4) increased concentration of the oil vapors; (5) decreased turbulence; and (6) increased space velocity except as effecting turbulence.

In addition to relative homogeneity of cracking which as defined would permit wide changes in cracking conditions during a, cycle, it is preferred that the cracking conditions also be what is termed herein relatively uniform during the cycle.

In a cyclic operation in which oil cracking chambers are heated during a heating period and the stored heat utilized during the cracking period, the quantity of oil gas produced (and the yields of the desired products) per gallon of oil during any individual oil-cracking run will vary somewhat as the temperature of the cracking environment decreases during said run. The degree of variation will depend among other factors, upon the length of the oil-cracking run, the oil, added aromatic hydrocarbon material and steam input rates, the presence or absence of supplementary heating during the run, the quantity of heat stored during the heating period and the character of the heat storage material.

Very large swings in oil gas production during a cycle are not preferred as any swing, in oil gas production during a cycle necessitates a departure from the optimum conditions within the range of the swing and makes the cracking less uniform over the cycle.

In the cyclic operation, other conditions being equal, swings in oil gas production during the cycle may be reduced by reducing temperature swings during the cycle which is favored by the use of a relatively short cycle and/or by the employment of highly conductive heat storage material.

Therefore, the environment of oil pyrolysis hereunder is advantageously arranged to provide not only relatively homogeneous cracking but also relatively uniform cracking.

A convenient measure of the homogeneity and uniformity of the cracking operation is the relation between the sulfonation residue and the free carbon in the condensate from the gas, as will hereinafter appear.

sulfonation residue is a measure of the normally non-gaseous paraifines and naphthenes surviving the cracking operation, and hence, high sulfonation residue is an indication of light cracking. Free carbon, on the other hand, is an end product in the pyrolysis of hydrocarbons and, hence, high free carbon indicates severe cracking.

High sulfonation residue together with high free carbon indicates that both light and severe cracking have taken place during the cycle and, hence, is an indication either of great lack of homogeneity of cracking, or of great lack of uniformity of cracking, or both.

Inasmuch as the determinations of sulfonation residue and free carbon depend upon the methods of analysis employed, detailed descriptions of the analyses used herein will be given hereinafter and herein when the terms sulfonation residue and free carbon are employed, they refer to the determinations obtained by said methods of analysis or by equivalent methods.

The present invention includes in addition to relatively homogeneous cracking and relatively uniform cracking, the adjustment of the oil pyrolyzing environment, including such factors as (1) temperature, and (2) effective time of contact, to obtain a desired intensity of cracking. Intensity of cracking is conveniently measured by the volume of "residual oil gas produced per gallon of oil pyrolyzed, although any other suitable method may be employed or devised.

In accordance with this invention the oil pyrolyzing environment is such that per gallon of oil pyrolyzed the volume of residual oil gas produced is maintained between 40 and 80 cubic feet taken as if measured at a pressure of 760 mm. and a temperature of 60 F., and preferably between 50 and 75 cubic feet under the same conditions of pressure and temperature.

Other conditions being the same, increase in either (1) temperature or (2) effective time of contact, or both, increases the volume of "residual oil gas per gallon of oil, and vice versa.

Residual oil gas is defined as the uncondensed final gas (composed of hydrocarbons and hydrogen) after removal of substantially all Water vapor or after correction for the presence of water vapor, and after the removal of substantially all hydrogen sulfide or after the correction for the presence of hydrogen sulfide (unless the ence of gas not derived from the total hydrocarbon material cracked (oil plus added aromatic hydrocarbon material), such as air, and combustion gases from fuel used for heating, and after correction for the presence of any water gas which may be present even though derived in part from the hydrocarbon material cracked. Procedure for making such corrections will be set forth in detail hereinafter.

The residual gas remaining after the above removal or correction will be referred to herein and in claims as residual oil gas.

Thus residual oil gasincludes gas derived not only from the petroleum oil pyrolyzed but also gas other than water gas derived from the added aromatic hydrocarbon material under the conditions of said pyrolysis.

Various procedures for the control of temperature in'cyclic gas-making sets are well understood by the skilled gas-maker. These include (1) adjustment of the length of the blast run; (2) adjustment of the rate of fuel consumption during the blast run; (3) adjustment of the length of the blast run with respect to the gas-making run or runs; (4) adjustment of the length of the purge or purges; (5) adjustment of the volume of steam or other gas used for purging; (6) adjustment of the length of the cycle; ('7) the use of a reverse run or runs and the adjustment of their length;

(8) the use of a reverse purge or purges; (9) the use of auxiliary heating means; (10) adjustment of the point of entry of secondary air and any tertiary air during the blast; and so forth.

Time of contact may be controlled by various factors, one of which is, of course, the dimensions including cross-sectional area, free space and length of the gas-making path of the set. In a given set the length of the gas-making path is more or less fixed and the same applies to the diameters of the various parts thereof such as the diameter of the interior of the carburetter, the diameter of the connection between the carburetter and the superheater, and the diameter of the superheater. With a given oil, added aromatic hydrocarbon material and steam rate the time of contact may be increased and decreased with increase and decrease respectively of the free space through which the vapors flow, for example, by adjusting the quantity and arrangement of the checker-brick employed.

Time of contact may also be adjusted by adjusting the oil and added aromatic hydrocarbon material rate or the steam rate, or both as will be obvious since the larger the combined volume of the gases passing through the set the shorter the time of contact and vice versa.

The rate at which the oil and added aromatic hydrocarbon material are vaporized in the set,

points of steam admission are to be considered Thus it will be seen that, although any exact mathematical determination of time of contact would be extremely involved, the control of the oil, added aromatic hydrocarbon material, and

steam rates, the control of the point, or points of entry of oil, added aromatic hydrocarbon material and steam, and the control of the amount and arrangement of checkerbrick, each alone or in combination, affords to the skilled gas-maker a fairly flexible control of time of contact.

All such factors will be wellunderstood by the skilled gas-maker, making it possible for him, upon becoming familiar with this invention, to readily adjust the operation of his set to yield residual oil gas within the ranges in volume specifically set forth above. Provided conditions of 1) relatively homogeneous cracking and (2) relatively uniform cracking are maintained, the volume of residual oil gas, as above defined per gallon of petroleum oil pyrolyzed is a dependable, convenient and substantially accurate yardstick of (3) the intensity of cracking.

Since the intensity (or depth or degree) of cracking depends on many factors, such for ininstance, as true temperature of the vapors and as, the effective time of contact, the concentration of vapors of the oil and added aromatic hydrocarbon material, the presence of catalysts and possibly other environmental conditions, it is extremely difficult of measurement by any means available at the present time other than based upon the gas produced. The true temperature, for example, may vary from the observed temperature according to some function of the factors influencing effective time of contact, which in turn may vary from calculated time of contact depending on functions of space velocity, turbulence and the surface-volume relationships of the cracking vessels. True temperature may also vary from observed temperature because of factors involving the pyrometers employed and their positions in relationship to the lining or other heat storage materials in the cracking vessels. It is obvious that many permutations of these factors may be made.

However, if the cracking is (1) relatively homogeneous and (2) relatively uniform, the volume of residual oil gas as above defined, is a measure which correlates these environmental factors and gives a convenient and accurate index of (3) the intensity of cracking.

It is as such an index that it is employed herein. The specific volumes of residual oil gas per gallon of petroleum oil recited have no utility per se except as a measure of a range of intensity of cracking, just as certain heights of mercury in a thermometer may have no utility except as a measure of a range of temperatures.

If the cracking is not (1) relatively homogeneous and not (2) relatively uniform," the volume of residual oil gas per gallon of petroleum oil pyrolyzed is not an accurate measure of (3) the intensity of cracking as the gas may then e composed of large portions of highly cracked material and large portions of lightly cracked material.

To summarize, broadly speaking this invention comprises pyrolyzing (1) a selected oil" of the character described (2) preferably in the presence of said certain added aromatic hydrocarbon material; and under conditions of (3) "relatively homogeneous cracking" and (4) "relatively uniform cracking," and with (5) the intensity of cracking such that (6) the "residual oil gas falls within the range above given.

The selected oil is predominately parafilnic or intermediate as defined by one or more of the means to be hereinafter more particularly described.

"Relatively homogeneous cracking conditions and "relatively uniform cracking" conditions are defined by the relationship between "sulfonation residue and free carbon, which relationship will also be hereinafter more particularly described and illustrated in the drawings. Residual oil gas determines the "intensity of cracking and means for determining residual oil gas will also be hereinafter more particularly described.

For convenience, the invention will be further illustrated in connection with the drawings which form a part of this specification for determining the relationship between sulfonation residue and free carbon, and illustrate apparatus in which the invention may be conveniently performed, and in which:

Figure 1 shows an elevation partly in section, diagrammatically illustrating a cyclic gas-making set;

Figure 2 shows curves defining maxima for the sulfonation residuefree carbon relationship.

Referring to Figure 1: This figure illustrates diagrammatically apparatus in which the invention may be performed and comprises a cyclic gas-making set.

i indicates a generator, 2 is a carburetter, 3 is a superheater, and 4 a wash box.' The generator i is provided with a burner generally'indicated at 5 with means for supplying fluid fuel such as tar, generally indicated at 6, and with means for supplying air for combustion of the fuel generally indicated at l. The generator may be provided with secondary air supply means as at 8. 9 indicates checkerbrick arranged above the combustion space I0. II, l2, and I3 are steam supply pipes.

The generator i is connected at its upper portion to the upper portion of the carburetter 2 by connection I4. The carburetter is illustrated as devoid of checkerbrick and is provided with oil supply means I 5 provided with a nozzle i5 capable of finely atomizing the oil. The carburetter is illustrated as also provided with aromatic hydrocarbon material supply means He provided with nozzle Ilia.

The carburetter 2 is connected at its base with the base of the superheater 3 by connection H.

The superheater 3 is shown provided with the checkerbrick indicated conventionally at l8. ()fitake 19 provided with valve 20 leads from the top of the superheater to the wash box 8, from whence connection 20a provided with valve 2| leads to condensate recover equipment and a gas relief holder (not shown).

The superheater is further provided with a stack valve 22 and may be provided with a steam supply means such as steam pipe 23. Air supply means such as 24 may be provided for admitting tertiary air to the superheater.

The generator i may be provided with the gas oil'take 25 provided with valve 26 and leading from the lower portion of the generator I to the wash box 4.

The refractory linings of the carburetter chamber and the superheater indicated at 21 and 28 respectively, as well as the checker brick such as in the superheater may if desired be of carhorundum or other highly heat conductive material instead of the clay fire brick customarily employed for this purpose. The use of relatively highly heat conductive refractory material, an outstanding example of which is carborundum or silicon carbide, is especially advantageous from the standpoint of obtaining uniformity of cracking since among other things the swing in temperature during any given cycle is thus considerably reduced as compared to the swing when clay fire brick is used.

The carburetter may be provided with checkerbrick as well as the superheater. Checkerbrick in the carburetter if employed are preferably fiued rather than staggered to decrease the percentage of liquid to be pyrolyzed coming into contact with heated surfaces prior to vaporization. An empty carburetter functions very'satisfactorily in this respect.

On the other hand, checkerbrick or its equivalent is definitely preferred in the superheater.

Thus it is preferred to provide a relatively low surface/volume ratio in the vaporizing zone and a relatively high surface/volume ratio in the cracking zone.

Other fluid fuel than tar may be employed for heating the generator I, such for instance, as oil or gas. Further, the generator may be provided with a grate and solid fuel burned thereon for heating instead of fluid fuel, if desired.

Thermocouples such as the shielded thermocouples 29, 30, 3|, 32 and 33 may be provided at spaced intervals through the vaporizing and cracking chambers, their connections leading to temperature recorders (not shown).

An illustrative cycle of operation of the apparatus of Figure 1 will be given.

In operation of the apparatus of Figure 1, fluid fuel such as tar, oil or gas is admitted to the generator burner and burned in the generator, with air supplied through pipe 1. Secondar air may be supplied through air supply pipe 8. The burning products pass from the generator to the carburetter 2 by way of connection I4 and thence through the carburetter to the superheater by way of connection l1. Tertiary air may be supplied through air supply means 24, if desired. The combustion products pass through the superheater and through the stack valve 22 to atmosphere or to a waste heat boiler (not shown). During this operation, the stack valve 22 is open and valve 26 is closed.

This operation, termed the blow, heats and stores heat in the checkerbrlck and lining of the generator, the lining of the carburetter and the checkerbrick and lining of the superheater.

The tar may then be shut off and a short air purge made by air admitted through air supply means 1, followed by a short steam purge with steam supplied to the base of the generator as at l3. The purged products pass out of the set through the stack valve 22.

After the set is purged, and with the stack valve 22 closed, valve 26 closed, and valves 20 and 2| open, petroleum oil selected as previously and hereinafter further described, is admitted to the carburetter top and finely atomized by the nozzle 16 into the void space of the carburetter.

Aromatic hydrocarbon material of the character previously described is admitted to the carburetter top during the oil admission and atomized by the nozzle l6a.

Simultaneously with the oil and added aromatic hydrocarbon material admission, steam is admitted to the generator through the steam supply l3 in the generator base, heated in passage through the generator checkerbrick and passed into the carburetter top by way of connection H. A portion or all of the steam may be admitted 10 through the steam supply means l2 at the gem erator top above the checkerbrick, instead of through ill at the bottom, and/or the temperature of the steam may be controlled by proportioning the quantities admitted to the two portions of the generator.

If desired, the added aromatic hydrocarbon material, in whole or in part, may be mixed with the oil and admitted therewith through supply means l5, or otherwise.

The oil and added aromatic hydrocarbon material are vaporized in thecarburetter in the presence of the superheated steam from the generator, the quantity of steam being sufficient to materially reduce the partial pressure of the oil vapors.

The vaporized oil, added aromatic hydrocarbon material and steam pass down through the carburetter and into the superheater through connection l1. Some cracking may take place in the carburetter.

From the base of the superheater the vaporized hydrocarbons, steam and partially cracked hydrocarbon vapors pass upward through the superheater checkerbrick in which the desired pyrolysis is completed.

The reaction products andsteam pass through connection IS, the wash box 4, and connection 20 to a relief holder (not shown), and thence through condensing or other apparatus (not shown) for the removal of the desired products from the gas.

After this operation, termed the run, the oil and added aromatic hydrocarbon material admission may be discontinuedand the reaction products purged from the set by steam admitted -to the generator, the reaction products being purged into the relief holder through the wash box.

The cycle may then be repeated. The above cycle is merely illustrative, it may be very greatly modified. For instance, a back run with steam or steam and oil or steam and oil and added aromatic hydrocarbon material may be made during the cycle, with steam or steam and oil or steam and oil and added aromatic hydrocarbon material supplied, for example, through supply means 23. In such case, th stack valve 22 is closed, valve 20 is closed and valve 26 open. The steam or steam and oil or steam and oil and added aromatic hydrocarbon material vapors and reaction products pass reversely through the superheater, carburetter and generator and through connection 26 to the wash box and to the relief holder (not shown).

Th fluid fuel burner as a means of providing heat during the blow is preferred, but recourse might be made to the use of a solid fuel bed as in the conventional water gas generator, with the difference that it is preferred not to pass any large quantity of water gas through the carburetter and superheater during the oil cracking period. Other means for superheating steam for the process might be then employed or saturated steam employed. The use of superheated steam, however, is preferred as it reduces the heating load on the carburetter.

During the blow, the operation is conducted to obtain the desired distribution of heat throughout the carburetter and superheater.

The following table will illustrate a typical swing in temperature at various points in a given set during a typical blow in the process of the invention. The temperatures were determined by the standard shielded type of thermocouple.

Table I Temperature, Temperature, Point in Set F. Start F. End of oi Blow Blow (Ilarburetter top l, 493 l, 787 carburetter middle. 1, 460 l, 740 Buperheater base l, 458 1, 542 Buperheater middle. 1, 450 1, 490 Superheater top 1, 433 l, 447

The temperature gradient throughout the set will vary with operating conditions and the nature and size of the set and the set lining and checkerbrick or other heat storage material.

In the case of set lining and other refractory material present, this is in a measure associated with the relative heat conductivity thereof. For instance, the substitution of refractory brick made of silicon carbide for refractory brick made of ordinary fire clay will shift the temperature gradient of the set and other conditions being equal will reduce the temperature swing throughout the cycle.

The temperature gradient naturally set up by the blow may be modified prior to the run by the injection of steam or other fluids to the top of the carburetter and/or the base and/or top of the superheater and/or to the generator. It may be employed to remove peak temperatures. This is described and claimed in copending application Serial Number 191,441, filed February 19, 1938, by Edwin L. Hall, which has matured into Patent 2,372,197, granted March 2'7, 1945.

The point or points of introduction of the oil and/or added aromatic hydrocarbon material may vary in different gas making equipment, from those chosen for illustration.

A carburetter devoid of checkerbrick is preferred for use in vaporizing the liquid hydrocarbon charge, but checkerbrick may be employed therein. The oil and added aromatic hydrocarbon material whether coming into contact with refractory surfaces in significant quantity or not are subjected to the temperatures of the carburetter and superheater with the steam and are decomposed in a manner essentially different from the decomposition of oil when the principal object is gas making, or when the principal object is the production of motor fuel.

The temperatures given above are purely illustrative in character and the temperature conditions as well as other conditions governing pyrolysis will vary with different types of operation or equipment.

As previously pointed out, having selected a predominantly parafllnic oil, or an intermediate oil, its pyrolysis is controlled by the gas maker, (modifying the interior of his set in accordance with the above observations if he finds it necessary or desirable), such that (l) the relationship between sulfonation residue and free carbon does not exceed certain maxima and (2) the residual oil gas falls within the range given. The relationship between sulfonation residue and free carbon determines (a) relatively homoge-' neous and (b) relatively uniform cracking conditions and the residual oil gas determines (c) the intensity of cracking.

Since determinations of Sulfonation residue and free carbon may vary somewhat with the methods of analysis employed, detailed procedures of analyses for these respective factors will be given herein, it being understood that values for sulfonation residue and for free carbon as expressed in the claims are to be determined by these detailed procedures, or their equivalents for definitive purposes, and that other yardsticks might be devised for the same purpose without departing from the invention.

An overall sample of the tar (wet) resulting during the pyrolysis of a known quantity of oil and obtained by condensation from the resulting gas by bringing the gas down to a temperature of approximately F. is heated in a batch in a still pot with stirring and with some reflux 0f the heavier distillate until a dry residual tar having a viscosity of 1000 S. S. U. at 210 F. is obtained. It usually requires several hours to remove the water from the tar.

After separation of the water layer, sulfonation residue is determined upon the hydrocarbon distillate obtained, and is expressed as per cent of the original oil by volume.

Free carbon is determined upon the dry residual tar and is expressed in per cent of the original oil by weight.

Free carbon determination is as follows.

Determination of free carbon Free carbon is determined in the manner described in The Gas Chemists Handbook, 3rd edition, 1929, a publication of the American Gas Association, pages 425 and 426.

Sulfonation residue determination is as follows.

Determination of sulfonation residue 250 mi. sample of the above hydrocarbon distillate is shaken with 5% by volume (12.5 mls.) of 94% H2804 in a 500 ml. separatory funnel.

The acid is gradually and cautiously added and the temperature kept below 25 C. by immersing the funnel in ice water when necessary.

After the reaction is completed the contents of the flask are transferred in approximately equal portions to each of two small separatory funnels (150 ml. Squibb separatory funnels).

The acid-washed oil is then centrifuged in the smaller funnels for approximately five minutes at 500-600 R. P. M. using a laboratory centrifuge adapted to accommodate these funnels.

The acid sludge is run oil slowly from each funnel into 200 mls. of ice water contained in a beaker. The acid sludge will sink to the bottom of the beaker and disperse into the water when stirred. The first drop of oil will spread over the surface of ,the water showing that the end of sludge separation has been reached.

The contents remaining in the funnels are then washed with two successive portions of about 5% by volume of water, followed by centrifuging for two minutes at 500-600 R. P. M. and the separated ,wash water run off.

The oil is then washed with two successive portions of 5% by volume of 20% KOH solution followed by centrifuging for two minutes at 500-600 R. P. M. and separation of the alkaline solution.

A final wash of 5% by volume of water is made followed by centrifuging for two minutes at 500-600 R. P. M. and separation of the wash water.

The oil is dried by adding a few granules of 4-mesh anhydrous calcium chloride, and filtering, and the volume of dry oil measured.

mls. of the washed and dried oil are distilled in the following manner. The oil is put in a 200 ml. round bottom Pyrex boiling flask. The flask is then connected with a small Hempel distilling tube using a cork stopper. The top of the distilling tube is fitted with a two-hole cork stopper containing a. thermometer C. to +360 C. in 1 C. intervals, 75 mm. immersion) and a drawn-out capillary tube extending to the bottom of the flask. The purpose of the capillary tube is to admit a small stream of air during vacuum distillation for the purpose of preventing bumping.

The outlet of the Hempel distilling tube is connected to a Liebig condenser. The outlet of the condenser is connected to a Bogert distilling receiver. The pressure at which the vacuum distillation is conducted is regulated at the outlet of the Bogert receiver by means of a suitable type needle valve.

Any suitable vacuum pump may reduce the pressure to 30 mm. mercury for the final distillation.

Distillation is made at two pressures-(a) oil boiling up to 160 C. is distilled off at atmospheric pressure, and (b) higher boiling fractions are distilled at 30 mm. mercury pressure and the distillation stopped when the temperature reaches 270 C.

If the material being distilled shows any of the characteristic signs of decomposition before the temperature of 270 C. is reached, the distillation is discontinued. The oil boiling up to 160 C. at atmospheric pressure is removed from the Bogert receiver before starting the vacuum distillation. Low pressure steam should be available for use in melting any naphthalene accumulations which may cause stoppages in the condenser tube.

The two distillates are mixed and the total volume recorded. sulfonation residue tests are mad on m1. portions of the mixture in a Babcock milk testing bottle with 30 mls. of 100% H2804 added, followed by heating and shaking periods (six ten-minute heating periods at 98-100 0., each of which is followed by a twominute shaking period). Any unsulfonated oil is floated into the neck of the Babcock bottle with 94% H2504 where its volume is measured. This quantity of material expressed as a percentage by volume of the original oil is the per cent sulfonation residue employed herein.

Referring to Figure 2. I

In this figure, per cent sulfonation residue as above determined and defined is plotted against per cent free carbon as above determined and defined.

The area to the left and below curve A embraces the relations between sulfonation residue and free carbon defining relatively homogeneous and relatively uniform crackingcondi-tions hereunder.

Preferably cracking conditions are selected to produce relationships between sulfonation residue and free carbon falling within the area to the left and below curve B.

More preferably cracking conditions are selected to produce relationships between sulfonation residue and free carbon falling within the area to the left and below curve C.

Still more preferably cracking conditions are selected to produce relationships between sulfonation residue and free carbon falling within the area to the left and below curve D.

The area to the right and above curve A embraces relationships between sulfonation residue and free carbon which define relatively nonhomogeneous and/or relatively non-uniform cracking conditions hereunder.

The formulae for curves A, B, C and D are as follows:

be used to 14 Curve A X(y0.03)=0.35 Curve B X(u0.03)-=0.25 Curve 0 X"(u0.03 =0.15 Curve D X(1 -0.03) =0.10

In which X=Per cent free carbon as above described and defined.

ll =Per cent sulfonation residue as above decribed and defined.

Moving to the right from the area to the left and below curve D, to the area between curves D and C, thence to the area between curves C and B, and thence to the area between curves B and A. relationships of sulfonation residue and free carbon are encountered which progressively define less homogeneous and/or less uniform cracking conditions. To the right and above curve A. these relationships are such as to no longer define relatively homogeneous and relatively uniform cracking hereunder.

Within the respective areas defined sulfonation residue and free carbon may vary considerably.

Under conditions of relatively high sulfonation residue higher yields of dienes are usually obtained and under conditions of relatively high free carbon with consequent relatively low sulfonation residue, the yields of aromatic hydrocarbons of improved quality are higher.

Since the latter type of operation may be consistent with good yields of dienes, it is frequently preferred and may be defined in terms of the sulfonation residue obtained.

Thus, it is usually preferred to operate with sulfonation residues substantially below 1% and more preferably substantially below 0.5% still more preferably below 0.1%.

Under such conditions the yields of dienes may be good while the yields of aromatic hydrocarbons of good quality are considerably improved.

As previously stated the present invention includes adjusting the oil pyrolyzing environment including such factors as temperature, effective time of contact and concentration of oil vapors so that per gallon of oil the total volume of "residual oil gas produced after the removal of substantially all water vapor, Or after correction for the presence of water vapor; and after the removal of substantially all hydrogen sulfide, or after the correction for the presence of hydrogen sulfide (unless the oil is low in sulfur content, in which case the hydrogen sulfide is negligible for calculation of residual oil gas"); and after removal of substantially all hydrocarbons having more than three carbon atoms, or after correction for the presence of hydrocarbons having more than three carbon atoms; and after correction for the presence of gas not derived from the total hydrocarbon material cracked (petroleum oil plus added aromatic hydrocarbon material) such as air, and combustion gases from fuel used for heating, and after the correction for the presence of any water gas which may be present even though derived in part from the hydrocarbon material cracked; is maintained between 40 and cubic feet taken as if measured at a pressure of 760 mm. and a temperature of 60 F., and preferably between 50 and '75 cubic feet under the same conditions of pressure and temperature.

Thevolume of residual oil gas may be calculated as follows:

Determination of residual oil gas The gas may be metered and sampled at any convenient stage in its condensation and purificaand tion, preferably however after purification from HzS. Water vapor is removed from a measured portion of the sample and the water vapor content of the gas calculated in per cent of the gas by volume, according to methods set forth in the Gas Chemists Handbook, 3rd edition, 1929, a publication of the American Gas Association, or their equivalent. The dried portion of the sample may be analyzed by low temperature fractionation as by means of the well known Podbelniak gas analysis apparatus or its equivalent. This apparatus has been described in Industrial and Engineering Chemistry, Analytical Edition, March 15, April 15, and May 15, 1933 and its use in hydrocarbon gas analysis is very well known to those skilled in the art,

By the above means, the dried sample may be divided into four portions: (1) containing H2, N2, 02, C0, C02, CH4, and any HzS, CS2, HCN, S02, NH; present, (2) containing C2 hydrocarbons such as C2H4 and C2H6, (3) containing C3 hydrocarbons such as CsHs and Cal-Ia, and (4) containing C4 hydrocarbons and hydrocarbons of higher carbon content. The per cent by volume relationship of these portions to the original undried gas may be readily calculated.

Another measured portion of the original sample may be analyzed for HzS according to methods described in the above mentioned Gas Chemists Handbook. From the analysis the percentage of H28 by volume in the gas as metered may be readily calculated.

Portion (1) may be analyzed for H2, N2, 02, CO and CO2, by means of the well known Hempel apparatus or its equivalent by methods described in the above mentioned Gas Chemists Handbook or their equivalents which methods include the initial removal of HzS and the percentage by volume of these constituents in the gas as metered calculated. 1

All of the N2, 02 and a portion of the CO2 are considered to be derived from air and combustion gases. The CO, the remainder of the CO2 and a portion of the H2 are considered to be derived from any water gas present. The remainder of the H2 is considered to be part of the oil gas. The method of apportionment of the CO2 between combustion gas and water gas and of the H2 between water gas and oil gas is as follows:

Per cent water gas=per cent CO+pcr cont H,

(W. G.)+per cent CO (W. G)

The above apportionment of CO2 and H2 is known to be approximate as the percentages of CO and CO2 in water 'gas vary with the temperature of its generation. The approximation is however sufficiently accurate for the purpose of calculating the residual oil gas.

The CS2, S02, HCN, and NH3 contents of the gas may be assumed to be negligible in the calculation of the residual oil gas unless these materials are known to be present in significant quantities which is usually not the case.

If the gas be metered and sampled after the usual HzS purification, the H23 may be assumed to be negligible for this calculation also, as the usual HzS purification removes practically all of the H28 as well as HCN and S02.

If the oil employed is not high in sulphur coritent, the 1128 may be negligible for the calculatlon of residual oil gas even before HzS purification.

When employing low sulphur oils the H28 content of the gas prior to His purification may be of the order of 50 grains per 100 cu. ft., equivalent to approximately .08% by volume, which would be insignificant.

If a high sulfur oil is employed the H28 content of the gas prior to HzS removal might not be negligible in the calculation of residual oil gas and therefore if the gas be metered and sampled prior to HzS purification the H28 content should be determined and the volume of HzS deducted in calculating the residual oil gas.

From the volume of total gas in cubic feet as metered and the volume of oil pyrolyzed in its manufacture, in gallons, the cubic feet of total gas per gallon of oil under the pressure and temperature conditions of metering may be readily calculated. The volume of total gas per gallon of oil is for convenience called V1.

V1 per cent air and combustion gases=cubic feet of air and combustion gases per gallon of 0i1=Vz Vi per cent of water gas=cubic feet of water gas per gallon of oil=V3 V1 per cent C4 hydrocarbon and higher=cubic feet of C4 hydrocarbons and higher per gallon of oil=V4 V1 per cent Water vapor=cubic feet of water vapor per gallon of oil=V5 V1 per cent H2S=cubic feet of H28 per gallon of Ol1=V6 oil gas per gallon of oil under the pressure and temperature conditions of metering=Vw If P=gas pressure as metered in mm. Hg and T=gas temperature as metered in F. absolute.

V7XP 519.6

If the gas is metered and analyzed after the usual HzS purification V6 need not be deducted or calculated.

If the gas be metered and analyzed after condensation of substantially all of the C4 hydrocarbons, the volume V4 will be very small and the volume of water vapor V5 will be negligible, and both may, under such circumstances, be neglected without introducing substantial error.

For purposes of calculating residual oil gas, a sharp separation between hydrocarbons of three carbon atoms and hydrocarbons of four carbon atoms is not found to be essential, since even if a fair percentage of the hydrocarbons of four carbon atoms is left in the gas the total volume of residual oil gas is not greatly increased.

Due to the difficulty of condensing hydrocarbons of three carbon atoms or lower, no large portions of these hydrocarbons will ordinarily condense along with the hydrocarbons of four carbon atoms and higher.

As an example of homogeneous and uniform cracking the following is given:

Example I A cyclic cracking operation was carried on in a three shell set connected in series similar to that diagrammatically illustrated in Figure 1. The carburetter and superheater were 2'9" in internal 17 diameter. The carburetter was approximately 9'5" long inside and the superheater was approximately 16'9" long inside. They were connected at their bases by a connection 1'0" internal diameter and 2'6 long. Both carburetter and superheater were lined with Carborundum refractory brick. The carburetter was devoid of checkerbrick. The superheater was provided with 29 courses of Carborundum checkerbrick of standard size 4 x 9" x 2%" set edgewise 3" apart with alternate courses in staggered relationship.

The cycle length was 3 minutes, 45% of which was occupied in heating and 33% by the oil and added aromatic hydrocarbon material admission period, the remaining portions of the cycle were devoted to purges of combustion products and of oil gas.

The oil selected in accordance with this invention, was a Texas crude oil from the East Texas field, a number 4 oil according to the Bureau of Mines Index to be hereinafter more particularly described, and having a Conradson carbon content below 4%. The oil was admitted to the carburetter top during the run at a rate of 4.03 gals.

per minute with steam (heated in the generator) at a rate of 30.9 lbs. per minute.

Simultaneously with the oil admission benzol was admitted to the carburetter top at a rate of 1.04 gals. per minute.

The average of temperatures observed by shielded thermocouples at spaced intervals through the carburetter and superheater was 1528 F.

The yield of residual oil gas per gallon of oil was 55.5 cubic feet. The sulfonation residue, determined as above described was just below 0.06%. The free carbon, determined as above described, was just below 0.64%.

The relationship between sulfonation residue and free carbon is expressed by the point E in Figure 2.

Very little if any difilculty was experienced with the handling of the tar emulsion in the wash box and in the condensers.

As an example of the homogeneous cracking of a predominantly naphthenic oil the following may be given:

Example 2 A cyclic cracking operation was carried on in the same three shell set as Example 1.

The cycle length was 3 minutes of which 46% was occupied in heating, 33% in the oil admission period and the remainder in purges of the apparatus of blast products and of oil gas.

The oil was a Texas Coastal Crude oil from the Placedo field, a #7 oil according to the Bureau of Mines classification, to be hereinafter more particularly described, and having a Conradson carbon content of less than 4%. It was admitted at a rate of 4.03 gals. per minute, and steam was admitted with the oil at a rate of 30.7 lbs. per minute.

The average of temperatures observed by shielded thermocouples at spaced intervals through the carburetter and superheater was 1525 F.

The residual oil gas yield was 55.9 cubic feet per gallon of oil. The sulfonation residue determined as above described was nil. The per cent free carbon determined as above described was just below 0.29%. This relationship of sulfonation residue and free carbon is expressed by the point F in Figure 2.

Example 3 An operation similar to that of Example 1 was performed in the same three shell set but without the admission of added aromatic hydrocarbon material.

The average of observed temperatures at the same portions of the set was 1491 F.

The yield of residual oil gas was 58.4 cubic ft./gal. of oil. The sulfonation residue, determined as above described was just below 0.19%. The free carbon, determined as above described, was just below 0.78%.

The relationship between sulfonation residue and free carbon is expressed by the point G in Figure 2.

In Example 1 the total yields of alkylated and alkenated aromatic hydrocarbons wer not only higher than in Example 3 and approaching those of Example 2, but individual products were of higher quality. This is particularly true of non-resin forming aromatic hydrocarbons such as benzene, toluene and xylene, a fact which is of greatest importance industrially and is a wholly unexpected feature not shared by cracking processes generally, even though aromatic hydrocarbon material is added to tJh'e oil pyrolyzing environment.

As pointed out in our copending application we have discovered that a characteristic of the cracking of a #7 oil under the conditions set forth in Example 2 is that high quality aromatics are produced under moderate cracking conditions which are conducive to the production of good yields of dienes and of thermally unstable aromatic resin formers.

To be of high quality, aromatic hydrocarbons, among other things, should not be contaminated with relatively high percentages of similarly boiling aliphatic hydrocarbons. For example, nonresin forming aromatics such as benzene, toluene and xylene should not be contaminated with significant quantities of similarly boiling parafiinic hydrocarbons, and resinforming aromatic hydrocarbons to be used for the production of polymers of individual com-pounds, which is the practice in obtaining high quality resins, such as for example polystyrene, polymethyl styrene and polyindene, should not be unduly contaminated with similarly boiling olefinic, dioleflnic, and/or acetylenic compounds.

This is obtainable in Example 2 and to a comparable extent in Example 1, and to a lesser extent in Example 3, but in each instance to an unexpectedly larger extent than is the case when our conditions of homogeneity, uniformity, and intensity of cracking are not observed, as in the pyrolysis of petroleum oil generally in the prior art.

Furthermore, the improvement in the quality of the non-resin-forming aromatics obtained in Example 1 over those obtained in Example 3, by virtue of the addition of aromatic hydrocarbon material, is extremely surprising and wholly to be unexpected from anything contained in tih'e prior art.

The total yield of certain very desirable aromatic resin-forming hydrocarbons, namely, styrene, methyl styrene, and indene, was 21.6 pounds per gallons of oil in Example 1; 25.5 pounds per 100 gallons of oil in Example 2; and 16.3 pounds per 100 gallons of oil in Example 3. In Examples 1 and 2 these materials were in a form in which they could be readily purified for the production of high quality resins, whereas in Ex- 19 ample 3 contamination of a more diflicultly removable nature was present with consequent rediction in quality particularly in the case of certain roducts.

Furthermore, difiiculty was encountered in the handling of the tar emulsion in Exampl 3, whereas in Example 1 the tar emulsion could be handled without difficulty and in a manner comparable to the handling of tar emulsion in Example 2. This is in itself a very important and totally unexpected result.

Nevertheless, pyrolysis of oil for our purposes in accordance with the procedure of Example 3 is a very substantial improvement over prior art processes for the pyrolysis of #1 to #4 oils, in view of the very special conditions of homogeneity, uniformity and intensity of cracking observed, in that a, substantial production of alkylated and/or alkenated aromatic hydrocarbons and benzene is obtained in higher quality than in prior art processes with a nelatively high production of allphatic dienes, and in that for any given yield of aliphatic dienes obtained, the quality of the aromatic hydrocarbon material obtained therewith is higher than in prior art processes.

Thus, broadly speaking, the pyrolysis of #1 to #4 oils under tJh'e conditions set forth herein, even though no aromatic hydrocarbon material is added, is within the concept of this invention.

The total recovery of certain very desirable non-aromatic resin-forming hydrocarbons, namely, butadiene, isoprene and piperylene, was 26.7 pounds per 100 gallons of oil in the case of Example 1; and 23.5 pounds per 100 gallons of oil in the cas of Example 3.

The recovery of indene, methyl styrene, styrene, piperylene, isoprene and butadiene totaled 48.3 pounds per 100 gallons of oil in Example 1 as against 39.8 pounds in Example 3.

Referring now to the lower boiling alkylated aromatics, namely, toluene and solvent naphtha (principally xylenes) the total yield in Example 1 was 42.2 pounds per 100 gallons of oil; and 38.6 pounds per 100 gallons of oil in Example 3. In Example 1 these materials were considerably less contaminated. For example, the toluene obtained in Example 1 was readily purifiable for nitration purposes, whereas the toluene obtained in Example 3 was less easily purifiable for nitration purposes, though much more so than in prior art processes.

The quality and quantity of aromatic unsaturates boiling above 210 C. up to say 450 C. are much higher under the conditions of Example 1 than under the conditions of Example 3.

In Example 1 all of the feedbenzene was recovered and in addition 27.7 pounds of benzene per 100 gallons of oil as compared to the recovery of 39.6 pounds of benzene per 100 gallons of oil in Example 3.

From the foregoing comparisons the outstanding advantages of the use of added aromatic hydrocarbon material in our invention become readily apparent.

Due at least in part to the different thermal stabilities of the various products, it has not been found that any one set of operating conditions results in maximum production of all of the several products.

However, within the range of residual oil gas set forth, will be found high yields of various desirable products of good quality.

Referring now more particularly to the character of the oil pyrolyzed, as previously stated, this comprises crude petroleum oils or a i a le cut or cuts from crude petroleum oils which may be classed as predominately paraflinic or intermediate as determined by any one or more or a number of chosen methods of classification which will now be more particularly set forth.

Oil classification In the classification of a crude oil in accordance with the Bureau of Mines method disclosed in Bureau of Mines Bulletin #291, dated September 1928, as modified by Bureau of Mines Report of Investigations 3279, previously referred to, a given petroleum oil is subjected to fractional distillation and two cuts are collected, the first having a boiling range between 250 and 275 C. at atmospheric pressure, and the second having a boiling range between 325 and 350 C. at 40 mm. absolute pressure.

For convenience of identification, the lower boiling fraction is referred to as key fraction 1 and the higher boiling fraction is referred to as key fraction 2.

From the API gravities of these key fractions, the classification of the original oil is made as follows:

If the API gravity of key fraction 1 is below 33, the fraction is classified as naphthenic; if it is between 33 and 40 the fraction is classified as intermediate; and if it is above 40 the fraction is classified as paraflinic.

If the API gravity of key fraction 2 is below 20, the fraction is classified as naphthenic; if it is between 20 and 30 the fraction is classified as intermediate; and if it is above 30 the fraction is classified as paraffinic.

As a result of the foregoing classifications of the key fractions, the original oil is given one of seven classifications as follows:

If both key fractions are parafiinic, the original oil falls in class 1. If key fraction 1 is parafllnic and key fraction 2 is intermediate, the original oil falls in class 2.

If key fraction 1 is intermediate and key fraction 2 is parafiinic the original oil falls in class 3.

If both key fractions are intermediate, the original oil falls in class 4.

If key fraction 1 is intermediate and key fraction 2 is naphthenic the original oil falls in class 5.

If key fraction 1 is naphthenic and key fraction 2 is intermediate the original oil falls in class 6.

If both key fractions are naphthenic, the original oil falls in class 7.

Based upon the foregoing classification in accordance with the present invention, we employ oils falling within the classes 1 to 4 inclusive, or desired cuts from such oils; with class 4 oils or a desired cut or cuts therefrom preferred, provided, however, that in the case of any oil selected whether a crude or a cut,. the Conradson carbon of the oil preferably does not exceed approximately 7% and preferably does not exceed approximately 4% The test for Conradson carbon has been standardized under the American Society of Testing Materials designation D189-36 and Conradson carbon as used herein is that Conradson carbon determined under such procedure.

The percentage of Conradson carbon is an indirect measure of the tendency of an oil to form carbon and hydrogen on pyrolysis instead of the valuable hydrocarbons desired.

Other things being equal in the pyrolysis of a crude oil, it is sometimes preferred to employ 22 I as determined with the F spectral line and the refractive index of the oil as determined with the C spectral line, employing a refractometer of the Abbe type.

Evaluation factor B. D. D. is a convenient measure of the ability of a petroleum oil to produce alkylated aromatic hydrocarbons such as solvent naphtha and toluene and aromatic resin formers such as styrene, methyl styrene and indene.

It has the advantage of applying to cuts from crude petroleum oils as well as the crudes, except such cuts as residuums too dark to permit the Average boiling point F.ll4)

Factor I 156-492(l0glog (no/4X 70.7

o Average boiling point F. 160) Factor II= 1004(sin arc tan HF cX104 65 Evaluation factor B. D. D.=factor IXfactor IIX 10- [156-492(l0glog [1004(sin arc tan The average boiling point employed is determined by making a modified straight run Engler distillation of the oil and observing the temperatures at which 30%, 50%, 70% and 85% by volume of the oil is taken off as vapor. The arithmetical average of these temperatures in T. is the average boiling point.

The general distillation procedure is that described in Gas ChemistsHandbook, 3rd edition (1929), pages '74 to '78, with the following exceptions.

The apparatus described is employed except that for the thermometer described there is substituted an A. S. T. M. general purpose thermometer (-7 60 F.) 3 inches immersion.

The procedure described is modified so that the determinations are made on a volume basis and temperatures are read at which 15%, 50%, 70% and 85% of the material is distilled over. Separation of cuts, determinations of their specific gravity, and coking determinations are unnecessary.

The preheating period should be not less than 10 minutes nor more than 20 minutes, higher boiling oils having the longer preheating.

The rate of distillation is carefully adjusted, by the needle valve on the burner, to 4 cc. per minute and this rate is maintained unless a slight drop in temperature accompanies a rate increase. (This will not usually occur below 500 F. and its occurrence indicates undesirable liquid phase cracking.) In this event, the heating is increased so that the thermometer is returned to its previous reading regardless of the rate. If the rate then decreases with constant increase in temperature, it is permitted to do so until a rate of 4 cc./min. is again reached. If the rate does not so decrease, the distillation is continued in such manner that the temperature constantly rises.

As before stated the arithmetical average of the five temperature readings is employed as the average boiling point. 7

The density (1 20/4 is determined by employing a Sprengel pycnometer. It is defined as the ratio of the weight in air of 5 cc. of oil at 20 C. to the weight in air of 5 cc. of water at 4 C.

The mean dispersion Hr-c is defined as the difference between the refractive index of the oil Average boiling point F. 114)] Average boiling point F. 1 HF cX104 65 -906 X10 3 determination of the mean dispersion, and residuums too heavy to permit the above determination of the average boiling point. Such residuums give very low yields of the desired products on pyrolysis.

When (HF-43X 10 is less than 65 it is assumed to be 65, so that the maximum value of factor II is 98.0 and so that negative values do not occur. Evaluation factor B. D. D. may be calculated directly from the formula or if desired it may be calculated by constructing monograms (not shown) expressing the equations of factors I and II.

A large number of crude oils ranging from Bureau of Mines class 1 oils to Bureau of Mines class 7 oils inclusive and cuts from certain of the crudes on examination gave evaluation factors B. D. D. ranging from 49.5 to 87.7, with factor I ranging from 39.0 to 93.0 and factor II ranging from 57.3 to 98.0.

The formulae for evaluation B. D. D. were empirically derived from petroleum oil characteristics and the results of petroleum oil pyrolysis. They are not intended to apply to the pyrolysis of individual pure hydrocarbons.

In accordance with the present invention, there is selected for pyrolysis hereunder, crude petroleum oils or cuts from such oils having evaluation factors B. D. D. not higher than 68 and preferably between 58 and 68.

If a given set is operated to crack (1) a petroleum oil selected as herein set forth, (2) preferably in the presence of said certain added aromatic hydrocarbon material, (3) relatively homogeneously and (4) relatively uniformly as herein defined, and (5) if the production of residual oil gas is held between the approximate limits above given. a substantially larger quantity of alkylated and alkenated aromatic hydrocarbons includin a substantially larger quantity of aromatic resinforming hydrocarbons, together with substantial quantities of other unsaturated resin-forming hydrocarbons and of non-resin-forming aromatic hydrocarbons are produced. and with a substantial reduction of parafilnes and non-aromatic olefines boiling within the ranges of the aromatic hydrocarbons.

In discussing the selection of petroleum oil for pyrolysis; it has been stated that a crude oil having the desired characteristics or a desired cut therefrom is employed. Heavy residuums unmixed with lighter cuts are preferably excluded.

The removal from the gas of hydrocarbons by condensation may be accomplished by any suitable means.

Generally speaking, there are four tools available for this purpose, namely, refrigeration, compression, absorption, such as in a scrubbing oil, and adsorption, such as on activated carbon. These may be used singly or in any desired combination.

The conjugated dienes of carbon atoms, namely. isoprene, piperylene, and cyclopentadiene may be separated from each other by any available means such as by the processes described and claimed in Patent 2,211,038 granted August 13, 1940, to Alger L. Ward, and in copending application Serial Number 342,910, filed June 28, 1940, by Alger L. Ward, which has matured into Patent 2,397,580, granted April 2, 1946.

' The unsaturated hydrocarbons of 4 carbon atoms, namely, butadiene and the butylenes may also be separated from each other by any available means such as by the processes described in the literature including granted patents.

The tar is processed for the recovery of light oil, dead oil and residual tar therefrom, either in a single combined body or in any selected portions according to the method of collection. Since steam is usually used in the pyrolysis of the oil, and since the resulting gas passes through the wash box 4 which contains water, the tar is usually collected in the form of an emulsion. This emulsion is usually brokenduring the treatment for the recovery of light oil, dead oil and residual tar.

Any means may be employed for the recovery of light oil, dead oil and residual tar from the original tar, such as the conventional tar dehydration procedure using batch distillation followed by fractionation of the distillate into light oil and dead oil. However, it is preferred to use more refined processes such as the process described in copending application Serial Number 342,735, filed June 2'7, 1940, by Edwin L. Hall and Howard R. Batchelder, which has matured into Patent 2,366,899, granted January 9, 1945, and Serial Number 353,034, filed August 17, 1940, by Howard R. Batchelder, which has matured into Patent 2,383,362, granted August 21, 1945.

The condensate collected from the various drip pots and from the holder is usually not in the form of an emulsion, and the various valuable hydrocarbons are recovered therefrom usually by distillation. If desired, the condensate drained from the various drip pots and from holder may be combined. On the other hand, this material may be combined with the light oil separated from the original tar and processed therewith.

Light oil recovered from the tar, and the condensate from the drip pots, and the holder, and the heavier hydrocarbon material are sources for benzene, alkylated benzenes such as toluene and the xylenes, for resin forming unsaturated hydrocarbons such as styrene, the methyl styrenes, dicyclopentadlene and indene as well as other valuable hydrocarbon material. Separations between these various hydrocarbons may be made by resorting to fractional distillation or other means to obtain relatively pure products or fractions in which the individual hydrocarbons specifically mentioned are concentrated.

Thus styrene may be separated in relatively pure form by special processing or by distillation into concentrated fractions which are preferably of at. least approximately 30% concentration, since below this concentration serious, contamination is present. Concentrations as high as approximately 60% or higher are obtainable by distillation and are especially preferred.

With indene the lower concentration is preferably at least approximately 50% and the higher concentration is at least approximately With the methyl styrenes as a group the respective percentages are approximately the same as with styrene, and with dicyclopentadiene the respective percentages are approximately the same as with indene.

In addition to high quality resin-forming unsaturated hydrocarbons, the light oil produced by the process described and claimed herein yields high quality benzene, toluene and solvent naphtha especially within the preferred range of "residual oil gas production.

Butadiene is concentrated in a fraction preferably of at least approximately 35% and especially of at least 50%.

The C5 diolefines, namely, isoprene, piperylene and cyclopentadiene, some of the latter in the form of its dimer dicyclopentadiene, which may be formed in the separation, are preferably separated by fractional distillation or otherwise, in a fraction of at least 30% concentration.

The dead oil depending upon the method of separation from the original tar may contain an unusually high percentage of very valuable aromatic resin-forming material which is extremely unusual. The dead oil also contains a large number of non-resin-forming hydrocarbons for example very valuable highly aromatic high boiling solvent oils, naphthalene, substituted naphthalene, anthracene, etc. An extremely surprising and wholly unexpected circumstance resulting from the use of added aromatic hydrocarbon material during the pyrolysis of the oil is that these oils are obtained in still higher yield and of still higher quality.

A high grade of residual tar is obtained, useful for the various purposes to which-material of this type is put.

It will be understood, however, that the particular description with respect to the removal of valuable hydrocarbons from the gas and their separation is for the purposes of illustration and that any other suitable system for this purpose might be substituted.

For some important uses of aromatic materials a low paraflln content is required. For example, in the nitration grades of benzene and toluene for the manufacture of explosives, such as picric acid and T. N. T., little paraflin content can be tolerated.

Olefinic material, produced in the pyrolysis and boiling in the neighborhood of the desired aromatic compounds, may be readily removed as by washing with sulfuric acid. The removal of small concentrations of paraflins boiling close to the boiling points of the desired aromatic compounds is very much more diflicult. In nitration toluene, the present U. S. Army specifications permit a paraflln content of not more than 1% by weight. In the production of toluene by the pyrolysis of petroleum oil, such a concentration of paraflinic material in a close toluene fraction means the production of an extremely small quantity of such material per gallon of oil pyrolyzed. If 0.30 lb. of toluene is produced per gallon of oil pyrolyzed, the above requirement means the production of less than 0.0003 lb. per gallon of oil of paraffins boiling in the nitration toluene range, or the removal of paraffins down to that quantity. In other words, it means a quantity of such paraffins less than from say 0.000039 lb. to 0.000046 lb. per lb. of oil pyrolyzed, depending upon the density of the 011.

Such extremely low yields of such parafflns usually may be realized in the pyrolysis of predominantly parafilnic or intermediate oils only by the employment of relatively severe cracking conditions. The tendency of such severe cracking conditions is to materially reduce the yields of valuable products, the production of which is favored by moderate cracking conditions. Among such products are alkylated aromatics, such as the xylenes and methyl styrene, and even more particularly the dienes, such as butadiene, isoprene, piperylene and cyclopentadiene. The yields of these dienes may virtually disappear under severe cracking conditions.

We have discovered that a careful regard to the homogeneity and the uniformity of the cracking operation, as practiced herein, enables the attainment of a given low paraifin content in the aromatic fractions of the products of pyrolysis, with less reduction in the yield of the more heat sensitive of the desired compounds.

Further than this, however, it has been found that if in conjunction with homogeneous and uniform cracking the predominantly parafiinic or intermediate oil is pyrolyzed in the presence of added aromatic material, such as benzene, for example, a low paraffin content in the aromatic hydrocarbon fractions of the products of pyrolysis, such for example as in a 2.5 or 1 toluene fraction, may be secured without the necessity of resorting to severe cracking conditions and without sacrificing yields of desired heat sensitive compounds to anything like the extent necessary in the absence of the added aromatic compound.

If the cracking is conducted homogeneously and uniformly, as previously described, and with an intensity such as to produce between 40 and 80 cu. ft. of residual oil gas per gallon of oil pyrolyzed and preferably between 50 and 70 cu. it, a quantity of aromatic material per gallon of oil pyrolyzed may be selected for addition to the oil pyrolyzing environment which will be sufficient to result in the reduction of the paraflinic material in the toluene fraction of the products of pyrolysis to below 1%, while still securing comparatively good yields of dienes.

The quantity of added aromatic material, such, for example, as benzol, required to be added for the purpose of thus sufliciently reducing the paraflin content of the toluene will usually decrease as the volume of residual oil gas produced increases, because an increase in the severity of the cracking of itself reduces the percentage of parafiinic material in the normally liquid portion of the products of pyrolysis.

Although as before stated, olefinic material boiling in the close neighborhood of the desired aromatic compounds may be removed readily by washing as with sulfuric acid, such washing may result in relatively high wash losses, when employing predominantly parafllnic or intermediate oils for pyrolysis. An additional advantage of the employment of added aromatic compounds in connection with the pyrolysis of such oils is a marked reduction in the concentration of olefinic material in the aromatic fractions of the products of pyrolysis. This is particularly true in the case of the benzol fractions, in which wash losses may be cut very considerably by the addition of aromatic material to the oil pyrolyzing environment.

Without the addition of aromatic material to the pyrolyzing environment and operating within the range of residual oil gas production per gallon of oil pyrolyzed, as previously set forth, benzene and toluene of nitration grade may be produced. However, it requires a greater intensity of cracking than if added aromatic material, such as benzol, is employed, and as before indicated, the tendency of a greater intensity of 'cracking is to reduce the yield of heat sensitive materials such as the dienes including butadiene, as well as the yield of such alkylated aromatic compounds as methyl styrene and the xylenes.

If a high yield of such material is not desired, it is entirely practicable to secure nitration grades of toluene and benzene from predominantly paraffinic and intermediate oils with good yields of styrene, and such aromatic compounds as naphthalene without the addition of aromatic material to oil pyrolyzing environment provided all other critical conditions of our invention are observed. It requires, however, a greater intensity of cracking than is necessary when employing redominantly naphthenic oils as described in our above-mentioned copending application, Serial N o.

372,074 filed December 28, 1940, which has matured into Patent No. 2,383,772, granted August 28, 1945.

Furthermore, the addition of aromatic hydrocarbon material to the oil pyrolysis environment under our previously described conditions of intensity of cracking and uniformity and homogeneity of cracking results in the production of relatively high boiling products of very high aromaticity. Both resin forming and non-resinforming fractions of very high aromaticity such as is characterized by mixed aniline numbers of 24 and as low as 20 and lower may be secured in fractions boiling in the boiling ranges such as from 210 C. to 350 C. and higher, 250 C. to 350 C. and higher, and 300 C. to 350 C. and higher.

The above mixed aniline numbers are as determined according to the procedure of ASTM D 611-41T, except that a hydrocarbon naphtha of 60 C. aniline point is employed as a diluent with the proportions 10 parts aniline, 2 /2 parts sample, and 2 /2 parts diluent. Equivalent procedure may be employed.

Such highly aromatic high boiling products are extremely valuable in rubber compounding especially in the compounding of synthetic rubber for the production of rubber having high resiliency at low temperatures, a characteristic particularly required of aviation rubber.

The aromatic hydrocarbon material may be added to the oil cracking environment at any desired point such as at the point of introduction of the petroleum oil, or at any other desired point or points such as directly into the zone of major cracking.

The additive need not be a pure substance but may comprise for example benzol, toluol, xylol, solvent naphtha or any other portion of light oil or even overall light oil itself.

However, particularly advantageous results are obtained when benzene itself or a fraction containing a substantial quantity of benzene such as a fraction preponderantly of benzene is used.

In view of equilibriumconsiderations there is a particular advantage in separating these products from the condensate produced and recycling 27 them to the oil pyrolyzing environment in which they were produced. Thus for example, benzol may be separated from the condensate and recycled back to the set in which the benzol was originally produced.

Any suitable quantity of aromatic hydrocarbon material may be added as for example, from or up to 25 or 50% or higher such as 100% of benzene by volume of oil pyrolyzed which term is used to include benzene containing material. to 45% is particularly suitable.

It has been found, that the net yield per gallon of oil pyrolyzed of a particular aromatic compound added to the oil pyrolyzing environment is usually less than the yield of that particular compound which is secured as a result of pyrolysis performed without such addition, all other conditions being the same.

By net yield is meant the total yield of the compound per gallon of oil pyrolyzed minus the quantity of the compound added per gallon of oil pyrolyzed.

Generally speaking, and other conditions being the same, the net yield per gallon of oil pyrolyzed of a particular aromatic compound decreases with an increase in the quantity of that compound added per gallon of oil pyrolyzed.

Generally speaking, if benzene is added, the net yield per gallon of oil of benzene tends to increase with increasing intensity of cracking, while if xylene is added the net yield per gallon of oil of xylene tends to decrease with increasing intensity of cracking.

Also generally speaking, the decrease due to the addition in net yield of the compound added, other conditions being equal, tends to be less in the case of benzene, than in the cases of toluene and xylene.

[156-492 (loglog d /4X l0 70.7

[1004(sin arc tan position of a selected petroleum oil by pyrolysis, it is conceivable that pyrolysis may be supplemented by other means for decomposing the oil of which catalysis is an example. In fact even in conventional gas making processes catalysis may unavoidably play a part in view of the heterogeneous character of the reactions involved and the possibility of many different materials being present. Thus, a combination of temperature and catalyst is within the purview of the invention in its broadest aspects.

Therefore, changes, omissions, additions, substitutions, and/or modifications might be made within the scope of the claims without departing from the spirit of the invention.

I claim:

1. In a cyclic process for the production of dienes with substantial yields of resin-forming aromatic hydrocarbons and non-resin forming aromatic hydrocarbons in which in one portion of the cycle heat is stored in a gas-making path by the passage of hot blast gases therethrough in contact with the surface of heat storage material arranged therein and in another portion of the cycle the stored heat is employed in the vapor phase pyrolysis of petroleum oil passed through said gas making path the steps which comprise pyrolyzing in said gas-making path in the presence of a substantial proportion of readily condensible diluent gas a petroleum oil selected from the group consisting of petroleum oils below 5 in classification of the Bureau of Mines Index and fractions thereof, said petroleum oil having an average boiling point-density-mean dispersion evaluation factor not higher than 68 as determined by the formula:

Evaluation factor:

Average boiling point F.- 160) 906 X10 2 Still generally speaking, the net yield of toluene in which 11 20/4 is the density of the oil at 20 C.

tends to be less responsive to changes in the intensity of cracking than the net yield of benzene and xylene.

The aromatic hydrocarbon additions preferably are restricted to materials which for the most part boil below 200 C,

While the invention has been more particularly described in connection with more or less conventional apparatus, it is to be understood that this is by way of illustration and that in its broad phases the invention may be employed with any suitable type of apparatus.

Furthermore, while in describing the invention the addition of aromatic hydrocarbon material during the pyrolysis has been especially emphasized, it is to be understood that it is this addition in combination with the other novel features of the invention which comprises the highly preferred manner of practicing the invention, producing results which are wholly unexpected from the addition of aromatic hydrocarbon material generally to oil pyrolyzing environments. The other features of the invention being novel in themselves are within the broad concept of this invention and are herein claimed generally, even though the better manner of their utilization is in combination with the addition of aromatic hydrocarbon material.

Additionally, while the invention has been described primarily in connection with the decomas compared with water at 4 C. and HF-C is the mean dispersion of the oil employing the F and C spectral lines, conducting said pyrolysis while re-v stricting the presence of any blue water gas to less than approximately 35 cubic feet of blue water gas per gallon of petroleum oil pyrolyzed, said cubic feet of blue water gas taken as if measured at a pressure of 760 mm. (Hg) and a temperature of 60 F. adjusting temperature and time of contact conditions and length and distribution of the cycle employed for said pyrolysis such that the volume of residual oil gas produced per gallon of petroleum oil pyrolyzed falls within the range of from 40 to cubic feet taken as if measured at a pressure of 760 mm. (Hg) and at a temperature of 60 F., and such that the relationship between the sulphonation residue and the free carbon obtained is within the sulphonation residue-free carbon relationships lying to the left oi. and below the curve defined by the equation X=(Y0.03)=0.35 in which X and Y are respectively rectangular coordinates of free carbon expressed in per cent by weight of the original oil pyrolyzed and sulphonation residue expressed in per cent by volume of the original oil pyrolyzed.

2. The process of claim 1 in which the volume of residual oil gas produced per gallon of petroleum oil pyrolyzed falls within the range of from 50 to 75 cubic feet taken as if measured at a pres- (mgmg d 20 4 10 40.7

[1004 (sin arc tan which X and Y are respectively rectangular coordinates of free carbon expressed in per cent by weight of the original oil pyrolyzed and sulphona- Lion residue expressed in percent by volume of the original oil pyrolyzed, and in which the value of Y is below 0.5%. s

3. The process of claim 1 in which the petroleum oil is pyrolyzed in the presence of from 5% to 50% by volume based on said petroleum oil of added aromatic hydrocarbon material boiling for the most part below 200 C., in which the relationship between the sulphonation residue and the free carbon obtained is within the sulphonation residue-free carbon relationships lying to the left of and below the curve defined by the equation X (Y0.03) =0.l in which X and Y are respectively rectangular coordinates of free carbon expressed in per cent by weight of the original oil pyrolyzed and sulphonation residue expressed in per cent by volume of the original oil pyrolyzed, and in which the value of Y is below 0.1%.

4. In a cyclic process for the production of dienes with substantial yields of resin-forming aromatic hydrocarbons and non-resin-forming aromatic hydrocarbons in which in one portion of the cycle heat is stored in a gas-making path by the passage of hot blast gases therethrough in contact with the surface of silicon carbide heat storage material arranged therein and in another portion of the cycle the stored heat is employed in the vapor phase pyrolysis of petroleum oil passed through said gas-making path the steps Average boiling point F. 114)] which comprise pyrolyzing in said gas-making v path in the presence of a substantial proportion of readily condensible diluent gas a petroleum oil selected from the group consisting of petroleum oils below 5 in classification of the Bureau of 30 Mines Index and fractions thereof, said petroleum oil having an average boiling point-densitymean dispersion evaluation factor not higher than 68 as determined by the formula:

Evaluation factor:

Average boiling point F. 160) 1 FcX-65 906 x 10 in which d /4 is the density of the oil at 20 C. as compared with water at 4 C. and HF-C is the mean dispersion of the oil employing the F and C spectral lines, conducting said pyrolysis while restricting the presence of any blue water gas to less than approximately cubic feet of blue water gas per gallon of petroleum oil pyrolyzed, said cubic feet of blue water gas taken as if measured at a pressure of 760 mm. (Hg) and a temperature of 60 F. adjusting temperature and time of contact conditions and length and distribution of the cycle employed for said pyrolysis such that the volume of residual oil gas produced per gallon of petroleum oil pyrolyzed falls within the range of from to 80 cubic feet taken as if measured at a pressure of 760 mm. (Hg) and at a temperature of F., and such that the relationship between the sulphonation residue and the free carbon obtained is within the sulphonation residue-free carbon relationships lying to the left of and below the curve defined by the equation X (Y0.03)=0.35 in which X and Y are respectively rectangular coordinates of free carbon expressed in per cent by weight of the original oil pyrolyzed and sulphonation residue expressed in per cent by volume of the original oil pyrolyzed.

NEWCOMB K. CHANEY. EDWIN L. HALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,218,495 Balcar Oct. 15, 1940 ,226,531 Chaney Dec. 31, 1940 

